Sustained intrathecal therapeutic protein delivery using genetically transduced tissue implants in a freely moving rat model.

Systemic delivery of therapeutic proteins to the central nervous system (CNS) is challenging because of the blood-brain barrier restrictions. Direct intrathecal delivery is possible but does not produce stable concentrations. We are proposing an alternative approach for localized delivery into the CNS based on the Transduced Autologous Restorative Gene Therapy (TARGT) system. This system was previously developed using a gene therapy approach with dermal tissue implants. Lewis rat dermal tissue was transduced to secrete human EPO (hEPO). TARGT viability and function were retained following cryopreservation. Upon implantation into the rat cisterna magna, a mild inflammatory response was observed at the TARGT-brain interface throughout 21-day implantation. hEPO expression was verified immunohistochemically and by secreted levels in cerebrospinal fluid (CSF), serum, and in vitro post explant. Detectable CSF hEPO levels were maintained during the study. Serum hEPO levels were similar to rat and human basal serum levels. In vitro, the highest hEPO concentration was observed on day 1 post-explant culture and then remained constant for over 21days. Prolonged incubation within the cisterna magna had no negative impact on TARGT hEPO secretion. These promising results suggest that TARGTs could be utilized for targeted delivery of therapeutic proteins to the CNS.

Behavior of poly(glycerol sebacate) plugs in chronic tympanic membrane perforations.

The tympanic membrane (TM), separating the external and middle ear, consists of fibrous connective tissue sandwiched between epithelial layers. To treat chronic ear infections, tympanostomy drainage tubes are placed in surgically created holes in TMs which can become chronic perforations upon extrusion. Perforations are repaired using a variety of techniques, but are limited by morbidity, unsatisfactory closure rates, or minimal regeneration of the connective tissue. A more effective, minimally-invasive therapy is necessary to enhance the perforation closure rate. Current research utilizing decellularized or alignate materials moderately enhance closure but the native TM architecture is not restored. Poly(glycerol sebacate) (PGS) is a biocompatible elastomer which supports cell migration and enzymatically degrades in contact with vascularized tissue. PGS spool-shaped plugs were manufactured using a novel process. Using minimally invasive procedures, these elastomeric plugs were inserted into chronic chinchilla TM perforations. As previously reported, effective perforation closure occurred as both flange surfaces were covered by confluent cell layers; >90% of perforations were closed at 6-week postimplantation. This unique in vivo environment has little vascularized tissue. Consequently, PGS degradation was minimal over 16-week implantation, hindering regeneration of the TM fibrous connective tissue. PGS degradation must be enhanced to promote complete TM regeneration.

A new artificial nerve graft containing rolled Schwann cell monolayers.

This study hypothesized that introducing high numbers of Schwann cells in monolayers via a novel rolled graft architecture would promote robust nerve regeneration. The objective was to place adherent Schwann cells in artificial nerve grafts and to assess regeneration through the Schwann cell-laden grafts compared with that through acellular grafts and autografts. Schwann cells were isolated from neonatal Fisher rats. Small intestinal submucosa (SIS) was harvested from adult Fisher rats, cut into 7 mm x 8 cm pieces, and pinned out. Schwann cells were plated onto the strips, allowed to reach confluence, and subsequently rolled into a laminar structure and implanted across a 7-mm gap in the rat sciatic nerve (n = 12). Control animals received SIS conduits without Schwann cells (n = 11) or autograft repair (n = 12). At 10.5 weeks, functional regeneration through the Schwann cell-laden grafts, measured by both sciatic function index and extensor postural thrust testing, exceeded that through the cell-free grafts and approached that achieved through autografts. These results highlight the role of Schwann cells in nerve regeneration. Regenerative results approaching autograft levels in the Schwann cell-laden group suggest that this methodology may ultimately be useful in clinical nerve repair.

Dynamic seeding and in vitro culture of hepatocytes in a flow perfusion system.

Our laboratory has investigated hepatocyte transplantation using biodegradable polymer matrices as an alternative treatment to end-stage liver disease. One of the major limitations has been the insufficient survival of an adequate mass of transplanted cells. This study investigates a novel method of dynamic seeding and culture of hepatocytes in a flow perfusion system. In experiment I, hepatocytes were flow-seeded onto PGA scaffolds and cultured in a flow perfusion system for 24 h. Overall metabolic activity and distribution of cells were assessed by their ability to reduce MTT. DNA quantification was used to determine the number of cells attached. Culture medium was analyzed for albumin content. In Experiment II, hepatocyte/polymer constructs were cultured in a perfusion system for 2 and 7 days. The constructs were examined by SEM and histology. Culture medium was analyzed for albumin. In experiment I, an average of 4.4 X 10(6) cells attached to the scaffolds by DNA quantification. Cells maintained a high metabolic activity and secreted albumin at a rate of 13 pg/cell/day. In experiment II, SEM demonstrated successful attachment of hepatocytes on the scaffolds after 2 and 7 days. Cells appeared healthy on histology and maintained a high rate of albumin secretion through day 7. Hepatocytes can be dynamically seeded onto biodegradable polymers and survive with a high rate of albumin synthesis in the flow perfusion culture system.